Acid and Bases

Acid and Bases

Acid and Bases

Have a sour taste. Vinegar is a solution of acetic acid. Citrus fruits contain citric acid.
React with certain metals to produce hydrogen gas .
React with carbonates and bicarbonates to produce carbon dioxide gas
Bases
Have a bitter taste.
Feel slippery. Many soaps contain bases.

þ
Produce H + (as H
3
O + ) ions in water (the hydronium ion is a hydrogen ion attached to a water molecule)
þ
Taste sour
þ
Corrode metals
þ
Electrolytes
þ
React with bases to form a salt and water
þ pH is less than 7
þ
Turns blue litmus paper to red “Blue to Red A-CID”

Acid Nomenclature Review
No Oxygen 
Anion
Ending Acid Name
-ide hydro (stem) ic acid
-ate (stem) ic acid w/Oxygen
-ite (stem) ous acid
An easy way to remember which goes with which…
“In the cafeteria, you ATE something ICky”

Acid Nomenclature
Flowchart
ACIDS start with 'H'
2 elements 3 elements hydro- prefix
-ic ending no hydro prefix
-ate ending becomes
-ic ending
-ite ending becomes
-ous ending

• HBr
(aq)
• H
2
CO
3
• H
2
SO
3
 hydrobromic acid
 carbonic acid
 sulfurous acid

• HI
(aq)
• HCl
(aq)
• H
2
SO
3
• HNO
3
• HIO
4

 Produce OH ions in water
 Taste bitter, chalky
 Are electrolytes
 Feel soapy, slippery
 React with acids to form salts and water
 pH greater than 7
 Turns red litmus paper to blue “Basic Blue”

NaOH
KOH
Ba(OH)
2
Mg(OH)
2
Al(OH)
3 sodium hydroxide lye potassium hydroxide liquid soap barium hydroxide stabilizer for plastics magnesium hydroxide “MOM” Milk of magnesia aluminum hydroxide Maalox (antacid)

• Definition #1: Arrhenius (traditional)
Acids – produce H + ions (or hydronium ions H
3
O + )
Bases – produce OH ions
(problem: some bases don’t have hydroxide ions!)

Arrhenius acid is a substance that produces H + (H
3
O + ) in water
Arrhenius base is a substance that produces OH in water

• Definition #2: Brønsted – Lowry
Acids – proton donor
Bases – proton acceptor
A “proton” is really just a hydrogen atom that has lost it’s electron!

A Br ønsted-Lowry acid is a proton donor
A Br ønsted-Lowry base is a proton acceptor base acid conjugate acid conjugate base

NH
Base
3
+ H
2
O
Acid
NH
Acid
4
+ + OH -
Base

Label the acid, base, conjugate acid, and conjugate base in each reaction:
HCl + OH  Cl + H
2
O
H
2
O + H
2
SO
4
 HSO
4
+ H
3
O +

Definition #3 – Lewis
Lewis acid - a substance that accepts an electron pair
Lewis base - a substance that donates an electron pair

Lewis Acids & Bases
Formation of hydronium ion is also an excellent example.
••
••
O —H
H
••
O —H
H
+
H
H
ACID BASE
• Electron pair of the new O-H bond originates on the Lewis base.

Lewis Acid/Base Reaction

Lewis Acid-Base
Interactions in Biology
• The heme group in hemoglobin can interact with O
CO.
2 and
• The Fe ion in hemoglobin is a
Lewis acid
• O
2 and CO can act as Lewis bases
Heme group

The pH scale is a way of expressing the strength of acids and bases. Instead of using very small numbers, we just use the NEGATIVE power of 10 on the Molarity of the H +
(or OH ) ion.
Under 7 = acid
7 = neutral
Over 7 = base

pH = - log [H+]
The [ ] mean Molarity)
Example: If [H + ] = 1 X 10 -10 pH = - log 1 X 10 -10 pH = - (- 10) pH = 10
Example: If [H + ] = 1.8 X 10 -5 pH = - log 1.8 X 10 -5 pH = - (- 4.74) pH = 4.74
Molarity Means
# mol Solute per Liter Solvent

Find the pH of these:
1) A 0.15 M solution of
Hydrochloric acid
2) A 3.00 X 10 -7 M solution of Nitric acid

pH calculations – Solving for
H+
If the pH of Coke is 3.12, [H + ] = ???
Because pH = - log [H + ] then
- pH = log [H + ]
Take antilog (10 x ) of both sides and get
10 -pH = [H + ]
[H + ] = 10 -3.12
= 7.6 x 10 -4 M

pH calculations – Solving for H+
• A solution has a pH of 8.5. What is the
Molarity of hydrogen ions in the solution?
pH = - log [H + ]
8.5 = - log [H + ]
-8.5 = log [H + ]
Antilog -8.5 = antilog (log [H + ])
10 -8.5
= [H + ]
3.16 X 10 -9 = [H + ]

• Since acids and bases are opposites, pH and pOH are opposites!
• pOH is useful for changing bases to pH.
• pOH looks at the perspective of a base pOH = - log [OH ]
Since pH and pOH are on opposite ends, pH + pOH = 14

[H + ]
[OH ] pOH pH

• There are several ways to test pH
– Blue litmus paper (red = acid)
– Red litmus paper (blue = basic)
– pH paper (multi-colored)
– pH meter (7 is neutral, <7 acid, >7 base)
– Universal indicator (multi-colored)
– Indicators like phenolphthalein
– Natural indicators like red cabbage, radishes

• Tests the voltage of the electrolyte
• Converts the voltage to pH
• Very cheap, accurate
• Must be calibrated with a buffer solution

pH indicators
• Indicators are dyes that can be added that will change color in the presence of an acid or base.
• Some indicators only work in a specific range of pH
• Once the drops are added, the sample is ruined
• Some dyes are natural, like radish skin or red cabbage

1. Add solution from the buret.
2. Reagent (base) reacts with compound (acid) in solution in the flask.
3. Indicator shows when exact stoichiometric reaction has occurred.
(Acid = Base)
This is called
NEUTRALIZATION.

Preparing Solutions by
Dilution
A shortcut
M
1
• V
1
= M
2
• V
2

You try this dilution problem
• You have a stock bottle of hydrochloric acid, which is 12.1 M. You need 400 mL of 0.10 M HCl. How much of the acid and how much water will you need?

• used to find the concentration of a solution using a solution of known concentration
• analyte
– solution with unknown concentration
• titrant
– solution with known concentration
– also called a standard solution

• equivalence point- when equal numbers of moles of acid and moles of base are present
• end point- when the color of an indicator changes
• equivalence point is usually marked by the color change (end point) of an indicator

1. If 20.00ml of acidic drain cleaner is titrated completely by 18.02ml of 0.100M NaOH, what is the acid’s concentration?
2. A 25.1ml volume of KOH is titrated with
43.2ml of 0.150M H
2
SO
4
. What is the molarity of the KOH?
3. A volume of 34.0ml of 0.100M H
3
PO
4 neutralizes 25.0ml of Ba(OH)
2
. What is the concentration of the barium hydroxide?

• Add 10.0 ml of vinegar to the beaker. Add 4 drops of indicator B, phenolpthalein.
• Fill the buret with 1.00M NaOH. Record the starting volume.
• Titrate until the mixture turns pink & stays pink. Use the minimum of drops.
• Measure the final volume and determine the change in volume of the base.
• Use AMaVa = BMbVb to determine the molarity of the vinegar, HC2H3O2.